Sound amplifying system



May 20, 1941..

A." LE R uPToN SOUND AMPLIFYING SYSTEM Filed Sept. 20, 1939 Ff; .1. f

Patented May 20, 1941 UNITED STATES PATENT oFFicE soUNn Amma sYs'rEM um: Le my Upton. s1. man, Mo. application sentent zo, 193s, sensi No. 295,113

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This invention relates to sound amplifying systems.

Most buildings which have not had severe treatment for the correction or fixing of their acoustical properties have reasonable or a sympathetic sound vibration at a denn-ite frequency. 'I'hat is to say, when a certain tone is struck, usually a low tone, the building will vibrate in unison or in sympathy with the source of the tone. This, of course, produces a distortion of sound and makes the problem of sound ampliilcation a diilicult one in those buildings. This dimculty is especially present in large buildings of the arena type. where large volume must be used and where little or no attention has been given, or can be given economically, to improving their acoustical properties. An obiect of the present invention is to provide means in a sound amplifying system to avoid or to reduce to a minimum resonance or sympathetic sound vibrations in a building in which it is used. Other objects will be apparent from the following detail description, taken in connection with the accompanying drawing or diagram.

Fig. 1 is a diagram showing a system embodyimi` the present invention and Fig. 2 is a diagram showing a modification.

The system contemplates the use of a plurality of microphones I which are connected by lines 2 to a voltage amplifier 3 which includes mixer units, and which for convenience is referred to as a mixer. It will be understood that one or a plurality of microphones may be used and also that in place of a microphone the input may be connected to a radio or to a phonograph or other type of transmitter.

The output oi the mixer is connected by circuits to a plurality of amplifiers 4 in parallel. The connecting circuits between the mixer and the amplifier include the wires 5 and conductors 6. In practice the conductors 3 may be metallic shields for the wires l which shields are grounded as shown at 1. The wires 5 are connected respectively to the amplifiers 4 through condenser-s 8 and variable potentiometers 3.

By way of illustration and exempllcation, but not limita-tion, it may be explained that in actual practice it has been found satisfactory to use a mixer 3 and as ampliers 4, certain standard equipment available in the market and well understood in the art. For a mixer, voltage amplifier N11-4297, produced by RCA Manufacturing Co., Inc., of .Camden, New Jersey. and for amplifiers, 50v watt power amplifier B1-4288 produced by the same company, have given the results intended.

A low frequency loud speaker I0 is connected through a two-band lter to an amplifier 4; a circuit I2, I3 connecting the amplifier with the filter The filter I I has a high frequency terminal I4, a low frequency terminal I5 and a common terminal I6. The loud speaker I0 is connected by a line I1 to the common terminal I6. A Wire I8 complementary to the wire I1 leads to a resistor I9, connected by a wire 20 to the low frequency terminal I5 on the filter. The wire I8 also leads to a switch 2| which may connect the wire I8 either with a point 22 or a point 23. The point 22 is connected to the line I1 and the point 23 is connected by a wire 24 to the line 20. i i

It may now be understood that the switch 2| serves to satisfactorily connect or disconnect the loud speaker, whenever it is desired and in a manner so that its manipulation will not crack in the loud speaker. By turning the switch to contact the point 22 the resistance I9 is shunted and the speaker I0 is placed in circuit and in operation. When it is desired to disconnect the speaker III the switch 2| is turned so as to contact the point 23, thus shunting the speaker and placing the resistor I9 in circuit. When the switch 2| is open, the resistor i9 and loud speaker I0 will be placed in series, but this will cause no sound disturbances, the effect being merely to reduce the volume of sound. When the switch 2| ls turned from the contact 22 to the contact 23, the effect will be to change the circuit so that the speaker I0 and the resistor I9 will be in series momentarily until the contact. point 23 is reached, at which time the resistor I9 will be shunted and the speaker III will be placed effectively in circuit. This last movement of the switch in placing the loud speaker Ill in circuit will not result in any sound dis turbance.

The high frequency terminal |4 is connected by a by-pass line 25 through a resistor 26 to the line |1.

As illustrated in the diagram a high frequency loud speaker 21 is connected to each of the two remaining amplifiers 4, and as illustrated each of the high frequency loud speaker units are identical. Each of the ampliers 4 supplying the high frequency loud speakers 21 is connected by a circuit", 29 to a two-band iilter 30, similar to the filter II, and having a high frequency terminal 3|, a low frequency terminal 32 and a common terminal 33. The speaker 21 nent amplifier 4. Likewise the resistor l1 should i have a resistance equivalent to the rated impedance of its pertinent speaker 21.

While two-band filters have been shown, it may be understood that band-pass filters may be used.

While only one loud speaker is shown connected to one amplifier, or to one filter, it is understood in the art that in such cases a plurality of loud speakers may be connected either in series or parallel, proper consideration being given to their impedance. In that case, of course, the pertinent resistors, such as I8 and 2i, pertinent to loud speaker I0 and resistor I1 pertinent to loud speaker 2l, should have a resistance equal to the combined or equivalent rated impedance of the speakers with which they are used.

It may now be understood that in a typical installation the system may be operated as presently described. In the normal operation of the system the microphones may be picking up sounds which have no low tones in such volume as will cause distortion when reproduced on the loud speakers through resonances of the building. In that case the potentiometers 9 lwill be adjusted so as to give a balanced tone effect through the building in which the system is installed, and the loud speaker i0 will be in circuit with the switch 2i connected to the point 23. Upon the occurrence of low notes causing resonances, the volume through the loud speaker I0 will be cut down by adjustment of the pertinent potentiometer 9, even by bringing the potentiometer to no-output level, or the loud speaker4 lil may be disconnected entirely by turning the switch from the point 23 to the point 22. An operator skilled in acoustics will be able to know immediately what adjustments to make, and in fact will be able to forecast, especially after rehearsals, low notes such as the tone of a speaker or low tones of a vocalist or instrumental music, or even the deep calls and growls of wild animals, so as to adjust the system immediately in advance of its requirements. As assistance in making the adjustments, the operator may have notes made during a rehearsal and he has the sound and visual indicators 38 and 38a to guide him. Visual indicators 38 and 38a are connected to indicate the voltage in the circuits from the filters which may operate the speakers. 'I'he indicator 38 is connected to show the voltage in the circuit for the low frequency from the filter il. As specifically shown, it is connected to by-pass both the speaker I8 and the resistor I9. thus indicating the voltage in the line at all times. The indicator 38 may be connected, as by jacks, to by-pass either the resistor i! or the speaker III, or-as shown, both of them. Indicators 28a are connected to indicate the voltage in the circuits feeding the high frequency speakers 21.

These indicators are used as aids for proper adjustments. When the system is made ready for a performance, proper levels for the several indicatorsis noted by trial and error, and thereafter adjustments are made to keep the proper sate for low tones.

levels constant, so far as practicable. If the voltage indicated by all of them drop or rise simultaneously. the volume is regulated by the mixer input control. If some of them vary the level may be restored by adjustment of the pertinent potentiometer 8.

Furthermore, the visual indicator 88 is of importance when the speaker Il has been disconnected. The readings on that instrument. when compared with the proper levels previously ascertained by tests, will inform the operator as to whether the speaker Il may satisfactorily be placed in circuit.

In the diagram two loud speakers of high frequency have been shown with one low frequency speaker, and this-re1ationship will ordinarily be found satisfactory. although the relative values of the low frequency and high frequency speakers may be adjusted to suit any particular requirement. It will also be understood that more than three amplifying units may be employed. In a typical installation four units of high frequency amplincation and two units of low frequency amplification are used. 'I'his installation is in an oval building in the form of an ellipse and employing four high frequency speakers and two low frequency speakers mounted together toward the ceiling in the center of the buiidmg.

The two low frequency amplifiers are oppositely directed along the major axis of the building or toward the end of the building, while the four high frequency speakers are directed, two toward the endsl of the building and two tcward the sides. That is to say, two high frequency ampliilers were oppositely directed along the minor axis of the building toward the sides while the other two are directed oppositely to each other along the major axis of the building toward the ends. This arrangement will serve to illustrate another advantage of the invention. The values of the several loud speakers are adjusted with respect to each other by adjusting the potentiom-v eters 8 so that each loud speaker will deliver the volume required of it in order to give, as far as possible. the same volume in all parts of the building. In the particular illustration given. where the amplifiers are mounted in the center of an oval building, one pointed toward an end and the other toward a side, the 'volume required of the one pointed toward the side is less than that of the one pointed toward the end.

Adjustments may also be made to compensate for audience seating or body saturation. A building may be lled unevenly, thus requiring an adjustment to provide uniform volume. For instance, in an oval building the public, preferring the side seats, will fill them up before those in the ends of the building. After the beginning of a performance, adjustments can and should be made as the continued seating makes it desirable.

It may be understood, therefore, that an initial adjustment of the potentiometers 9 may be made so as to adjust the loud speakers to the situations in which theyare placed. After that an adjustment of the potentiometer 9 in the low frequency unit will serve to adjust the system to compen- Or the switch 2| may be used to cut out the low frequency speaker Il a1- together.

It may also be understood that in place of low frequency speaker l0 a high fidelity speaker reproducing both high and low frequencies may be used. In that case the speaker will be connected directly either temporarily or permanently to the circuit I2, I3 from the amplifier and the iilter I I will not be used.

Fig. 2 is a diagram showing a modification in which a high frequency speaker 39, as well as the low frequency speaker I0, is operated through the lter II. The high frequency speaker 39 is connected in series with the resistor 26. A Wire 40 is connected to one side of the speaker 39, .to one side of the resistor 26 and to a switch 4I. The switch 4I may connect the wire 40 either with a point 42 or a point 43. The point 42 is connected by a wire 44 to the line 25, and the point 43 is connected by a wire 45 to the line I1. The connection of the switcii 4I with the speaker 39 is the same as the relationship of the switch 2| to the low frequency speaker I0. By the switch 4I the speaker 39 may be connected or disconnected at will with no sound disturbance.

The un-it including the filter II, and the loud speakers I and 39 may be used alone without other lters or speakers.

It is contemplated that visual indicators, although omitted from Fig. 2, may be used as described heretofore to indicate the voltage in the lines supplying the speakers.

It will be obvious that various changes may be made in the details of construction, some of which have been suggested, within the scope of the appended claims, without departing from the spirit of this invention, that parts of the invention may be used without the whole, and that various additions and applications may be made.

I claim:

1. A sound amplifying system comprising sound pick-up means, a voltage amplier connected to said. pick-up means, a plurality of power amplifiers, circuits connecting said power amplifiers to said voltage amplifier, a variable potentiometer in each of said circuits, and -a vis- -ual indicator for registering voltage flowing to a loud speaker for the lower audio frequencies.

2. In a sound amplifying system, a plurality of loud speakers, circuits responsive to different audio frequencies for actuating said speakers, and visual indicators for registering the voltage in the circuits respectively.

3. In a sound amplifying system,`a plurality of loud speakers, circuits responsive to different audio frequencies for actuating said speakers, means for shunting at least some of said speakers, and visual indicators for registering the voltage in a circuit after its speaker has been shunted.

4. In a sound amplifying system, a high frequency loud speaker, a low frequency loud speaker. circuits responsive to high and low audio frequencies for actuating said speakers respectively, means for shunting the low frequency speaker, and a visual indicator for indicating the voltage -in said low frequency circuit when said low frequency speaker is shunted. 1

5. In a sound amplifying system, a loud speaker, a supply circuit therefor, a register connected in the circuit in series with the speaker and having a resistance equivalent to the rated impedance of the speaker, and a visual indicator for registering .the voltage in said circuit at least when the speaker is shunted.

6. A sound amplifying system comprising sound pick-up means, a voltage amplifier conpower amplifiers, circuits connecting said power ampliers in parallel to said' voltage amplifier, means for varying Ithe voltage independently in each of said circuits, loud speakers responsive to different -audio frequencies connected by separate circuits to the power ampllers respectively, and visual indicators in the last mentioned circuits for registering the voltage therein.

7. A sound amplifying system comprising sound pick-up means, a voltage amplifier connected to said pick-up means, a plurality of power ampl-iers, circuits connecting said power amplifiers in parallel to said voltage amplifier, means for varying the voltage independently, loud speakers for different audio frequencies connected by separate circuits to the power ampliers respectively, and means for shunting at least one of the speakers for lthe lower audio frequencies.

8. A n,sound amplifying system comprising sound pick-up means, a voltage amplifier connected to said pick-up means, a plurality of power ampliers, circuits connecting said power amp ers In parallel to said voltage ampliiier, mea s for varying the voltage independently in each of said circuits, loud speakers for different audio frequencies connected by separate circuits to the power amplifiers respectively, a resistance in the circuit supplying a speaker for lower audio frequencies in series with said speaker, and means for shunting said resistance and said speaker.

ALBERT LE ROY UPTON. 

